Recently, the aldehyde 4-oxo-2-nonenal (ONE) was identified as a product of lipid peroxidation and found to be an effective protein modifier. In this in vitro study we investigated structural implications of the interaction between ONE and alpha-synuclein, a protein which forms intraneuronal inclusions in neurodegenerative disorders such as Parkinson's disease and dementia with Lewy bodies. Our results demonstrate that ONE induced an almost complete conversion of monomeric alpha-synuclein into 40-80 nm wide and 6-8 nm high soluble beta-sheet-rich oligomers with a molecular weight of similar to 2000 kDa Further. more, the ONE-induced alpha-synuclein oligomers displayed a high stability and were not sensitive to treatment with sodium dodecyl sulfate, indicating that ONE stabilized the oligomers by cross-linking individual alpha-synuclein molecules. Despite prolonged incubation the oligomers did not continue to aggregate into a fibrillar state, thus suggesting that these alpha-synuclein species were not on a fibrillogenic pathway. (C) 2008 Elsevier Inc. All rights reserved